1. Field of the Invention
The present invention is generally related to x-ray imaging and more specifically to reduction of data included within a movement model based thereon.
2. Related Art
To prepare a radiation treatment plan for a patient, a physician may use a model representative of movement of a portion of the patient's body. This model is referred to as a movement model and is commonly used to target diseased areas during treatment. For example, in radiation therapy for treatment of lung cancer, respiratory movement of the patient during therapy can be accounted for using a movement model. This may improve the efficacy of the treatment.
To develop a movement model, a series of x-ray images are generated, each x-ray image being associated with a different time point. From these x-ray images, a series of deformation fields are calculated to describe the movement of points within the patient. This series of deformation fields is an example of a movement model. Methods of using these deformation fields to approximate positions of a patient's organs over a period of time are known in the art.
FIG. 1 illustrates a deformation field 120 generated from two x-ray images, 110 and 130 respectfully. X-ray images 110 and 130 are images of a chest recorded at two different time points. X-ray image 110 is slightly different than x-ray image 130 because the chest has expanded upward and outward slightly between the two different time points. Deformation field 120 is calculated based on x-ray images 110 and 130 using an image registration system and represents movement of imaged objects between the x-ray images. Such image registration systems are well known in the art. Deformation field 120 can be considered to be associated with one of the time points at which the x-ray images 110 and 130 were generated.
Deformation field 120 includes a plurality of vectors 140 representative of changes between x-ray images 110 and 130. These vectors may be two or three dimensional. While FIG. 1 illustrates thirty-two 2-dimentional vectors 140, in practice deformation field 120 can include a 3-dimensional vector for each pair of corresponding pixels in the x-ray images 110 and 130. For example, if x-ray images 110 and 130 each include 500 by 500 by 100 pixels, then deformation field 120 will include 500×500×100=25,000,000 vectors. Each of these vectors may be represented by up to twenty-four bytes of data. Therefore, each deformation field can require over 500 MB (megabytes) of storage.
A movement model may include ten or more deformation fields each requiring 500 MB of storage. In that case, a movement model including 10 deformation fields would require 500×10=5000 MB of storage. Storage of this movement model requires a large amount of memory. This is particularly a problem in clinical environments where thousands of movement models relating to different patients may be stored. There is, therefore, a need for a reduction in the large storage requirements of movement models.